Fly eye lens

ABSTRACT

A fly eye lens has cells in an optical functional portion, and first, second, and third positioning portions on an outer edge. The first and second positioning portions are located in a region of a plane normal to the optical axis of the lens, divided by a first reference line extending through a center of thermal expansion and located in the plane. The first and second positioning portions have side surfaces located on the first reference line. The third positioning portion has a side surface located on a second reference line intersecting the first reference line, extending through the center of thermal expansion, and located in the plane. Even when the fly eye lens thermally expands, the position of the center of thermal expansion does not change in an optical system, and desired optical performance can be continuously achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plastic fly eye lens used in anoptical system such as a liquid crystal projector.

2. Related Background Art

As conventional fly eye lenses, fly eye lenses B and C, employed in apair in a housing A of an optical system such as a liquid crystalprojector are known, as shown in FIG. 5. These fly eye lenses B and Crespectively have pluralities of cells E_(B) and E_(C), and light from alight source can uniformly irradiate a target object with the opticalfunction of the cells E_(B) and E_(C).

The fly eye lenses B and C are fitted in the housing A, fixed withretainers H extending through the housing A with their outer edgeportions abutting against projections F projecting on the inner surfaceof the housing A, and are positioned such that their lens surfacesperpendicularly intersect an optical axis Z of this optical system. Inthis state, when a lamp D emits light, this light is focused in units ofcells E_(B) of the fly eye lens B. The focused light is then receivedand enlarged in units of cells E_(C) of the fly eye lens C thatcorrespond to the cells E_(B) in one-to-one correspondence. The lightthus irradiates a target optical system G as uniform light.

In this conventional optical system, the interior of the optical systemis heated to a high temperature of 150° C. or more by irradiation withthe lamp D. The housing A and fly eye lenses B and C thus thermallyexpand, so desired optical performance cannot be obtained.

For example, when the coefficient of thermal expansion of the housing Ais larger than that of the fly eye lenses B and C, the housing A becomeslarger with respect to the fly eye lenses B and C. Then, a gap is formedbetween the inner wall of the housing A and the outer edges of the flyeye lenses B and C, and the centers of the fly eye lenses B and C areshifted from the optical axis Z. In this case, the centers of the twofly eye lenses B and C are also shifted from each other, and the opticalperformance may undesirably, largely degrade.

When the coefficient of thermal expansion of the housing A is smallerthan that of the fly eye lenses B and C, the fly eye lenses B and Cbecome larger with respect to the housing A. Thus, the fly eye lenses Band C are to expand by pushing the inner wall of the housing A.Therefore, the fly eye lenses B and C may be distorted, leading todegrading optical performance.

As a countermeasure for this inconvenience, a glass plate I coated withan anti-reflecting coating may be interposed as a heat-insulating memberbetween the lamp D and fly eye lens B, as shown in FIG. 6. However, asheat of the lamp D is conducted through the housing A and the like,thermal expansion of the housing A and fly eye lenses B and C cannot beprevented effectively.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems, andhas as its object to provide a fly eye lens which can obtain desiredoptical performance even if it thermally expands.

More specifically, according to the present invention, there is provideda fly eye lens with a plurality of cells at an optical functionalportion thereof, characterized by having first, second, and thirdpositioning portions on an outer edge thereof, wherein the first andsecond positioning portions are formed on one of regions of a planenormal to the optical axis of the lens, and divided by a first referenceline extending through a center of thermal expansion located on theplane of the lens, the first and second positioning portions having endportions located on the first reference line, and the third positioningportion has an end portion located on a second reference line crossingthe first reference line and extending through the center of thermalexpansion located on the plane of the lens.

According to the present invention, the fly eye lens is positioned withrespect to an optical system by using the end portions of the first,second, and third positioning portions. Even when the fly eye lensthermally expands, the end portions of its first and second positioningportions can be positioned on the first reference line and the endportion of its third positioning portion can be positioned on the secondreference line. Therefore, when the fly eye lens thermally expands, thecenter of its thermal expansion can be prevented from moving withrespect to the optical system, and degradation in optical functionresulted from movement of the fly eye lens can be prevented.

The fly eye lens according to the present invention can be characterizedin that the first, second, and third positioning portions describedabove are projections projecting from the outer edge of the fly eyelens, or recesses formed by recessing the outer edge of the fly eyelens. When the respective positioning portions are formed in thismanner, in addition to the function and effect described above, a gapthrough which heat in the optical system is discharged can be ensuredeasily.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not to beconsidered as limiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a fly eye lens according to apreferred embodiment of the present invention;

FIG. 2 is a front view of the fly eye lens shown in FIG. 1;

FIG. 3 is a front view showing the practical arrangement in an opticalsystem of the fly eye lens shown in FIG. 1;

FIG. 4 is a perspective view showing a fly eye lens according to anotherembodiment of the present invention;

FIG. 5 is a sectional view showing the basic arrangement of an opticalsystem using conventional fly eye lenses; and

FIG. 6 is a sectional view showing the basic arrangement of anotheroptical system using conventional fly eye lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fly eye lens according to a preferred embodiment of the presentinvention will be described in detail with reference to the accompanyingdrawings. In the following description, portions that are identical orequivalent to each other are denoted by the same reference numerals, anda repetitive description thereof will be omitted.

FIG. 1 is a perspective view showing a fly eye lens according to apreferred embodiment of the present invention. As shown in FIG. 1, a flyeye lens 10 according to this embodiment in a rectangular plate and ismade of a resin. An optical functional portion 20 is formed at thecenter of one surface of the fly eye lens 10, and corner portions 30 areformed around the optical functional portion 20. A plurality of cells 21are formed in the optical functional portion 20. The cells 21 serve asoptical convex lenses, and are arranged in a matrix.

First, second, and third positioning portions 40, 50, and 60 which formprismatic projections project from the outer edge of the fly eye lens10.

FIG. 2 is a front view for explaining the arrangement of the first,second, and third positioning portions 40, 50, and 60 of the fly eyelens 10 shown in FIG. 1.

The first positioning portion 40 is disposed on one side of therectangular outer edge of the fly eye lens 10, and the secondpositioning portion 50 is disposed on an opposite side to face the firstpositioning portion 40. The third positioning portion 60 is disposed onone remaining side of the outer edge where the first and secondpositioning portions 40 and 50 are not disposed.

The positioning portions 40 to 60 will be described in detail. The firstand second positioning portions 40 and 50 are located in one of regionsof a plane normal to the optical axis of the fly eye lens 10. Theregions are divided by a first reference line X extending through thecenter O of thermal expansion. The side surface of the first and secondpositioning portions 40 and 50 are located on the first reference lineX. The “center of thermal expansion” refers to a position serving as thecenter when the fly eye lens 10 thermally expands. The fly eye lens 10is preferably formed such that the center O of thermal expansion and thegeometric barycenter of the fly eye lens 10 coincide with each other.The first reference line X is a straight line extending through thecenter O of thermal expansion of the fly eye lens 10.

A side surface of the third positioning portion 60 is located on asecond reference line Y perpendicular to the first reference line X andextending through the center O of thermal expansion. Therefore, evenwhen the fly eye lens 10 thermally expands, the center O of thermalexpansion along the second reference line Y does not shift with respectto the first and second positioning portions 40 and 50. Also, the centerO of thermal expansion along the first reference line X does not shiftwith respect to the third positioning portion 60.

The fly eye lens 10 can be fabricated highly precisely by injectionmolding or press molding of a plastic material.

FIG. 3 is a sectional view of a practical arrangement obtained when thefly eye lens 10 of FIG. 1 is disposed in the housing A.

As shown in FIG. 3, a hollow portion a is formed in the housing A. Thehollow portion a is a space where optical component such as the fly eyelens 10 is to be arranged, and has, e.g., a rectangular section. Aprojection 41 projects from a side surface 45 of the hollow portion a. Aprojection 51 projects from a side surface 55 opposing the side surface45, to face the projection 41.

The projections 41 and 51 serve as abutting members with upper endportions against which the first positioning portions 40 and 50 are toabut. A projection 61 projects from a floor surface 65. The projection61 serves as an abutting member with a side portion against which theside portion of the third positioning portion 60 of the fly eye lens 10is to abut.

The first reference line X of the fly eye lens 10 is positioned withrespect to this housing A by the first positioning portion 40, theabutting surface of the projection 41, the second positioning portion50, and the abutting surface of the projection 51. The second referenceline Y of the fly eye lens 10 is positioned by the third positioningportion 60 and the abutting surface of the projection 61. With thisarrangement, the position of the center O of thermal expansion of thefly eye lens 10 is positioned with respect to the housing A.

When the positions of the projections 41, 51, and 61 are appropriatelyadjusted, the positions of an optical axis Z (not shown) of the opticalsystem and the center O of thermal expansion of the fly eye lens 10relative to each other can be determined easily if necessary, so thatthe optical axis Z (not shown) of the optical system and the center O ofthermal expansion of the fly eye lens 10 can be set to coincide witheach other.

A projection 42 projects above the projection 41 from the side surface45, and a spring 43 is provided to the lower end portion of theprojection 42. The spring 43 depresses from above the first positioningportion 40 of the fly eye lens 10 abutted by the projection 41, therebymaintaining the abutting state. Similarly, a projection 52 projectsabove the projection 51 from the side surface 55, and a spring 53 isprovided to the lower end portion of the projection 52. The spring 53depresses from above the second positioning portion 50 of the fly eyelens 10 abutted by the projection 51, thereby maintaining the abuttingstate.

A projection 62 projects from the floor surface 65 at a side opposite tothe projection 61 with respect to the third positioning portion 60 ofthe fly eye lens 10, and a spring 63 is provided to the side portion, onthe third positioning portion 60 side, of the projection 62. The spring63 depresses laterally the third positioning portion 60 of the fly eyelens 10 abutted by the projection 61, thereby maintaining the abuttingstate.

The sizes of the respective positioning portions of the fly eye lens 10and of the respective projections of the housing A are set byconsidering the differences among their coefficients of thermalexpansion. As shown in FIG. 3, predetermined gaps are formed between thedistal end portions of the respective positioning portions and therespective opposing side surfaces of the hollow portion a, and betweenthe distal end portions of the respective projections and the opposingouter edge of the fly eye lens 10.

In the state shown in FIG. 3, even when the interior in the housing A isheated to a high temperature and the fly eye lens 10 thermally expandscentered on the center O of thermal expansion, the first positioningportion 40 is depressed and supported by the projection 41, and thesecond positioning portion 50 is supported as it is depressed by theprojection 51. Therefore, the fly eye lens 10 can be supported whileallowing the first and second positioning portions 40 and 50 to movealong the second reference line Y.

Since the third positioning portion 60 is depressed and supported by theprojection 61, the fly eye lens 10 can be supported while allowing thethird positioning portion 60 to move along the second reference line Y.

Furthermore, gaps are formed between the distal ends of the second andthird positioning portions 50 and 60 and the inner wall of the housingA, and between the distal ends of the projections 41, 51, and 61 and theouter edge of the fly eye lens 10. Therefore, deformation of the fly eyelens 10, which occurs when the distal ends of the first, second, andthird positioning portions 40, 50, and 60 and the inner wall of thehousing A, and the distal ends of the projections 41, 51, and 61 and theouter edge of the fly eye lens 10, come into contact with each other,can be prevented.

In the state shown in FIG. 3, even when the interior of the housing A isheated to a high temperature and the fly eye lens 10 thermally expandscentered on the center O of thermal expansion, the first reference lineX determined by the first positioning portion 40 of the fly eye lens 10and the projection 41, and the second positioning portion 50 of the flyeye lens 10 and the projection 51 does not move along the secondreference line Y. Therefore, the center O of thermal expansion of thefly eye lens 10 can be prevented from being shifted in the housing Aalong the second reference line Y.

The second reference line Y determined by the third positioning portion60 of the fly eye lens 10 and the projection 61 does not move along thefirst reference line X. Therefore, the center O of thermal expansion ofthe fly eye lens 10 can be prevented from being shifted in the housing Aalong the first reference line X.

Hence, even if the interior of the housing A is heated to a hightemperature and the fly eye lens 10 thermally expands centered on thecenter O of thermal expansion, movement of the center O of thermalexpansion of the fly eye lens 10 with respect to the housing A can beprevented. If the center O of thermal expansion and the optical axis Zof the optical system are aligned in advance, the shift between them canbe prevented even under conditions with which thermal expansion occurs.

Due to the arrangements of the projections of the fly eye lens 10 andhousing A, a large gap, which cannot be conventionally obtained, can beensured between the fly eye lens 10 and housing A, as shown in FIG. 3,and this gap can be used as a good heat dissipation path. The good heatdissipating function of the arrangement itself, which is produced by thecombination of the fly eye lens 10 and housing A, also contributes topreventing degradation in optical function caused by thermal expansion.

How to use the fly eye lens 10 in an optical system such as a liquidcrystal projector will be described with reference to FIG. 3.

As a housing A where the fly eye lens 10 is disposed, one havingprojections 41, 42, 51, 52, 61, and 62 for positioning two fly eyelenses 10, that are formed such that the center of the housing A and anoptical axis Z (not shown) of this optical system coincide with eachother, is used. The fly eye lenses 10 are arranged such that theircenters O of thermal expansion and the optical axis Z of the opticalsystem coincide with each other. These fly eye lenses 10 are arranged ata predetermined gap such that they can exhibit desired opticalperformance.

For each fly eye lens 10, its first positioning portion 40 is depressedagainst the projection 41 by the spring 43, the second positioningportion 50 is depressed against the projection 51 by the spring 53, andthe third positioning portion 60 is depressed against the projection 61by the spring 63. Hence, the respective fly eye lenses 10 are positionedwith reference to the first and second reference lines X and Y.

In this state, when a lamp (not shown) arranged near one fly eye lens 10emits light, the emitted light propagates through the fly eye lenses 10.In this case, the housing A and the two fly eye lenses 10 thermallyexpand by heat emitted from the lamp.

However, the two fly eye lenses 10 positioned in the housing A thermallyexpand centered on the centers O of thermal expansion, while maintainingthe abutting state of each positioning portion and with the positions oftheir centers O of thermal expansion being kept immobile. Therefore, thepositions of the plurality of cells of the first fly eye lens 10, seenfrom the optical axis of the optical system, relative to the positionsof the plurality of cells of the second fly eye lens 10 which opticallyform pairs with the cells on the first fly eye lens 10 in units ofcells, are kept unchanged even when thermal expansion occurs.

More specifically, since the first and second fly eye lenses 10 are heldwith the optical axes of their cells which form the pairs being alignedwith each other, uniform radiation can be ideally, continuouslyperformed. If the center of thermal expansion of the fly eye lens 10 andthe optical axis Z of the optical system are aligned with each other inadvance, the positions of all the cells on the two fly eye lensesrelative to each other can be held with respect to the optical axis Z aswell. Therefore, these fly eye lenses 10 can be used also inapplications where strict conditions are required for the arrangement ofthe optical system.

FIG. 4 is a perspective view showing another practical arrangement of afly eye lens.

In the fly eye lens 10 described above, the respective positioningportions are projections projecting from the outer edge of the fly eyelens 10. In contrast to this, in a fly eye lens 10 a shown in FIG. 4,its respective positioning portions are recessed from its outer edge.Even with this arrangement, when this fly eye lens 10 a is positioned byfirst, second, and third positioning portions 40, 50, and 60, theposition of the center O of its thermal expansion is kept unchangedduring thermal expansion, and the fly eye lens 10 a can exhibit desiredoptical performance.

The center O of thermal expansion is not limited to the geometricbarycenter of the fly eye lens 10 or 10 a, but can be an arbitrary pointwhere the first and second reference lines X and Y determined by thefirst, second, and third positioning portions 40, 50, and 60perpendicularly intersect each other. In this case as well, when the flyeye lens 10 or 10 a disposed in an optical system thermally expands, itscenter O of thermal expansion does not move with respect to the opticalsystem. Therefore, desired optical performance can be obtained.

The preferred embodiment of the present invention has been described.Note that the present invention is not limited to the above embodiment.For example, the fly eye lens according to the present invention is notlimited for use in a liquid crystal projector, but can be used in otheroptical systems.

In the fly eye lens described above, the first and second referencelines X and Y perpendicularly intersect each other. However, in the flyeye lens according to the present invention, the first and secondreference lines X and Y need not perpendicularly intersect each other asfar as they cross each other. In this case as well, the same functionand effect as those obtained with the fly eye lens 10 or 10 a describedabove can be obtained. More specifically, when the fly eye lens isthermally expands, its movement on the first reference line along thesecond reference line is prevented, and its movement on the secondreference line along the first reference line is prevented. As a result,movement of the center of thermal expansion, where the first and secondreference lines cross each other, can be prevented reliably.

As has been described above, according to the present invention, a flyeye lens is positioned with respect to an optical system by using theend portions of the first, second, and third positioning portions. Evenwhen the fly eye lens thermally expands, the end portions of its firstand second positioning portions can be positioned on the first referenceline, and the end portion of its third positioning portion can bepositioned on the second reference line. Therefore, movement of thecenter of thermal expansion of the fly eye lens with respect to theoptical system, which is caused by thermal expansion of the fly eye lenscan be prevented, and degradation in optical function resulted frommovement of the fly eye lens can be prevented.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. A fly eye lens comprising: a plurality of cellsin an optical functional portion having an optical axis; and first,second, and third positioning portions on outer edges of said opticalfunctional portion wherein said first and second positioning portionsare located in one region of a plane normal to the optical axis of saidfly eye lens and divided into two regions by a first reference lineextending through a center of thermal expansion of said fly eye lens andlocated in the plane, said first and second positioning portions havingside surfaces located on the first reference line, and said thirdpositioning portion has a side surface located on a second referenceline intersecting the first reference line and extending through thecenter of thermal expansion located in the plane.
 2. The lens accordingto claim 1, wherein said first, second, and third positioning portionsare projections projecting from said outer edge.
 3. The lens accordingto claim 1, wherein said first, second and third positioning portionsare recesses in said outer edge.
 4. The lens according to claim 1,wherein the outer edge is rectangular and has four sides and the firstand second positioning portions are located on opposite sides of therectangular outer edge and the third positioning portion is located on aside of the rectangular outer edge different from the first and secondpositioning portions.